1. Field of the Invention
The present invention relates generally to ink-jet technology and, more particularly to a heated printing zone vacuum platen.
2. Description of the Related Art
The art of ink-jet technology is relatively well developed. Commercial products such as computer printers, graphics plotters, copiers, and facsimile machines employ ink-jet technology for producing hard copy. The basics of this technology are disclosed, for example, in various articles in the Hewlett-Packard Journal, Vol. 36, No. 5 (May 1985), Vol. 39, No. 4 (August 1988), Vol. 39, No. 5 (October 1988), Vol. 43, No. 4 (August 1992), Vol. 43, No. 6 (December 1992) and Vol. 45, No. 1 (February 1994) editions. Ink-jet devices are also described by W. J. Lloyd and H. T. Taub in OUTPUT HARDCOPY [sic] DEVICES, chapter 13 (Ed. R. C. Durbeck and S. Sherr, Academic Press, San Diego, 1988). As providing background information, the foregoing documents are incorporated herein by reference.
It is known to use a vacuum induced force to adhere a sheet of flexible material to a surface, for example, for holding a sheet of print media temporarily to a platen. [Hereinafter, "vacuum induced force" is also referred to as "vacuum induced flow," "vacuum flow," or more simply as just "vacuum" or "suction," as best fits the context.] Such vacuum holddown systems are a relatively common, economical technology to implement commercially and can improve hard copy apparatus throughput specifications. For example, it is known to provide a rotating drum with holes through the surface wherein a vacuum through the drum cylinder provides a suction force at the holes in the drum surface (see e.g., U.S. Pat. No. 4,237,466 (Scranton)). [The term "drum" as used hereinafter is intended to be synonymous with any curvilinear implementation incorporating the present invention; while the term "platen" can be defined as a flat holding surface, in hard copy technology it is also used for curvilinear surfaces, such as the ubiquitous typewriter rubber roller; thus, for the purposes of the present application, "platen" is used generically for any shape paper holddown surface used in a hard copy apparatus.] Permeable belts traversing a vacuum inducing support have been similarly employed (see e.g., Scranton and U.S. patent application Ser. No. 09/163,098 by Rasmussen et al. for a BELT DRIVEN MEDIA HANDLING SYSTEM WITH FEEDBACK CONTROL FOR IMPROVING MEDIA ADVANCE ACCURACY (assigned to the common assignee of the present invention and incorporated herein by reference)).
Generally in a hard copy apparatus implementation, the vacuum device is used either to support cut-sheet print media during transport to a printing station of a hard copy apparatus, to hold the sheet media at the printing station while images are formed (known as the "printing zone"), or both. [In order to simplify discussion, the term "paper" is used hereinafter to refer to all types of print media and the term "printer" to refer to all types of hard copy apparatus; no limitation on the scope of the invention is intended nor should any be implied.]
Typically thermal ink-jet inks are water-based and when deposited on wood-based papers, they are absorbed into the cellulose fibers, causing the fibers to swell. As the cellulose fibers swell, they generate localized expansions, causing the paper to cockle. Not only does this create a finished hard copy product that may be objectionable to the end-user, cockle growth can cause actual degradation of ink dot printing quality itself due to uncontrolled pen-to-paper spacing which may even, in turn, lead to pen printhead-to-paper contact as the cockle waves move a region of the paper upwardly.
Moreover, most commercial ink-jet printers allow the paper to exit the printing zone on a flat platen or into a substantially flat output tray while the ink is drying. A flat platen with no post-printing holddown mechanism allows cockle to expand, generally creating larger waves in the sheet of paper.
Furthermore, in order to produce high quality color copy, e.g., photo-quality printing, ink flux is increased to produce vivid color saturation. This flux increase further exacerbates the paper cockle problem.
Still further, ink-jet printhead size is increasing to increase throughput. As the print zone length increases, ink bleed effects and the paper cockle problem are again enlarged or intensified.
Several solutions to these problems have been developed. U.S. Pat. No. 4,329,295 (Medin et al.) for a PRINT ZONE HEATER SCREEN FOR THERMAL INK-JET PRINTER, U.S. Pat. No. 5,461,408 (Giles et al.) for a DUAL FEED PAPER PATH FOR INK-JET PRINTER, U.S. Pat. No. 5,399,039 (Giles et al.) for an INK-JET PRINTER WITH PRECISE PRINT ZONE MEDIA CONTROL, U.S. Pat. No. 5,420,621 (Richtsmeier et al.) for a DOUBLE STAR WHEEL FOR POST-PRINTING MEDIA CONTROL IN INKJET PRINTING, and Des. Pat. No. 358,417 (Medin et al.) (each is assigned to the common assignee of the present invention and incorporated herein by reference) exemplify various techniques for a hard copy apparatus using conventional electromechanical paper feed systems. U.S. Pat. No. 5,742,315 (Szlucha et al.) shows a SEGMENTED FLEXIBLE HEATER FOR DRYING A PRINTED IMAGE. A segmented flexible heater is disposed adjacently to a paper path for heating a recording medium before and during printing.
There remains a need for print zone and post-print zone paper path transport mechanisms that assist in reducing the expanding paper cockle problem. One solution is to hold the paper to a platen with a vacuum force during printing. However, it has been found that with vacuum holding creates a higher frequency, or "sharper" looking, cockle wave in the paper. The geometric complexities of designing a vacuum transport type apparatus compounded by the heating of the transported flexible material creates a need for improved heat distribution mechanisms. In ink-jet printing applications, there is a need for vacuum holddown paper path systems that assist in reducing or substantially eliminating paper cockle.